Noise cancelling headphones vs ear defenders?

So, like many of you, I have a problem with extraneous noise, in fact, any noise that *I* haven't chosen. To help with this I've been looking at solutions. When I'm listening to an audiobook or a podcast, I wear earbuds which are great at blocking out (most) external noise, allowing me to only hear what I'm playing, but there are times when I don't want to listen to *any* sounds at all, so my earbuds are useless then. I've bought myself a pair of ear defenders which work brilliantly (and they've already saved a life! I longer have an uncontrollable urge to strangle my partner when she suddenly plays a Facebook video at full blast! Lol!). However, someone mentioned noise cancelling headphones to me as a better alternative and I'm wondering what your thoughts are, one versus the other? I'm not 100% sure how NC headphones work. I know they emit sound waves that supposedly cancels out the same external sound waves at anything before a certain pitch (apparently, they don't work well on kids voices..), but I've also read that you can still hear conversation if you're talking to someone, but not the TV in the background, for instance. Can anyone give first hand info on whether any of that is correct?